The present invention relates to a method for monitoring a torque of an electric motor, in particular for application in a motor vehicle, wherein the electric motor is supplied with electric current in multiple phases, wherein a first torque value of the torque which is output by the electric motor is determined on the basis of an electric power which is taken up by the electric motor and a detected rotational speed of the rotor of the electric motor.
According to a second aspect the present invention relates to a method for monitoring a torque of an electric motor, in particular for application in a motor vehicle, wherein the electric motor is supplied with electric current in multiple phases, wherein below a predefined rotational speed of a rotor of the electric motor a first torque value of the torque which is output by the electric motor is determined on the basis of an amplitude of at least one phase current.
The present invention also relates to a device for monitoring a torque of an electric motor with current-detecting means for detecting at least one phase current of the electric motor, rotor-detecting means for detecting a rotational position and/or a rotational speed of a rotor of the electric motor, and a control unit which is designed to carry out the method specified at the beginning
Finally, the present invention relates to a motor vehicle drive train having at least one electric machine for making available drive power and a device of the type specified above.
In the field of electric motor technology, it is generally known to check the state of an electric motor and to determine an output variable, such as for example the torque which is output by the electric motor, and compare it with a setpoint state. By comparing the actual state with the setpoint state it is possible here to monitor the operation of the electric machine in order to react correspondingly in the event of deviation of the actual state from the setpoint state.
The torque which is output by the electric motor is usually calculated on the basis of an electric power which is extracted from a direct voltage source and a rotational speed of the rotor of the electric motor. In this context, the electric power which is extracted from the direct voltage source is calculated by means of the electrical voltage made available and an electric current which is detected by means of a direct current sensor.
DE 10 2008 001 714 A1 discloses a method in which the electric power which is taken up by the electric motor or a cross current which is the cause for the torque is detected and linked to a characteristic curve of a rotational speed of the electric motor in order to determine the present torque and compare it with a setpoint value.
A disadvantage with the methods known from the prior art is that due to the direct current sensor for determining the taken-up electric power the method is highly technically complex and measuring errors cannot be detected or taken into account during the determination of the torque which is output.
The object of the present invention is therefore to make available a method and a device for monitoring a torque of an electric machine which provides increased reliability with low technical complexity.